Impact of wildfires on spatial and temporal evolution of groundwater recharge in an Atlantic pine forest: An integrated approach using field, remote sensing and modeling.

Leiria Pine Forest (Portugal) Climate change, including higher temperatures, drier atmosphere and prolonged droughts, is increasing the risk, extent and impacts of wildfires in Southern Europe. This study investigates extreme wildfires impacts on groundwater recharge in the Leiria Pine Forest, integrating field and remote sensing data with modelling tools to simulate recharge in burnt and unburnt areas from 2001 to 2023. show a decline in crop-adjusted potential evapotranspiration due to vegetation loss after the fire, resulting in increased recharge rates. Groundwater recharge increased from 20 % of annual precipitation pre-fire to over 40 % in the first-year post-fire in the burnt area, gradually stabilizing at around 30 % by 2023. This contrasts with the unburnt area, where recharge rates remained stable. This increase is influenced by geological and pedological characteristics, favorable topography which promotes low runoff and high infiltration rates, and specific climatic conditions. The low water-holding capacity of the sandy arenosols in the burnt area, promotes faster infiltration, increasing recharge. Contrary to other studies, soil water repellence seems to have limited influence in this area due to local climate and soil conditions. Predicting the consequences of wildfires in groundwater is complex process, nevertheless the application of multiple methodologies increases result reliability. • The wildfire burned over 85 % of the forest, causing significant land use changes and altering the hydrological conditions. • Remote sensing tools help overcome temporal and spatial data limitations in assessing wildfire impacts. • Groundwater recharge in the burnt area increased from 20 % to 40 % of precipitation in the first year after the wildfire. • Six years after the wildfire, groundwater levels in the burnt area remain 10 % higher than historical averages. • Evapotranspiration and landscape changes determine the overall recharge response to wildfires.